1. Field of the Invention
The invention relates in general to a liquid crystal display, and more particularly to a lamp drive circuit that balance the currents for the lamp.
2. Description of the Related Art
Liquid crystal display normally adopts the structure of using a set of drive circuits 100 to drive a lamp. The lamp used in the backlight module of the liquid crystal display is used for providing a light source when a liquid crystal display displays. As shown in FIG. 1, a diagram of a conventional lamp drive circuit is shown. A set of drive circuits 100 include a direct current power DC, a switch 102 and the transformer 104. The switch 102 is used for converting the direct voltage outputted by the direct current power DC into an alternate (alternating (AC)) voltage to the transformer 104, so that the transformer 104 accordingly generates the alternate voltage level capable of driving the lamp 106.
Along with the increase in the size of the liquid crystal display, the large-sized liquid crystal TV for instance, the backlight module has to provide a higher luminance so as to maintain the display quality. In order to improve the luminance of the backlight module, not only the size of the lamp needs to be enlarged, but also the number of the lamp used needs to be increased.
In order to reduce the cost of driving a number of lamps, a conventional practice is to drive a number of lamps by a set of drive circuits 100. Referring to FIG. 2, a diagram of another example of the conventional lamp drive circuit is shown. By electrically connecting a number of lamps 106 (1)˜106 (N) connected in parallel, where N is a positive integer, fewer transformers 104 and switches 102 are used, so that the costs are reduced.
Despite the above practice reduces costs, the application is subject to the characteristics of the lamps 106. That is, the impedance of each lamp 106 is different, so that each current flowing through each lamp 106 is different. Consequently, each lamp 106 is different luminance, resulting in a non-informal distribution of the luminance of the backlight module which deteriorates the display quality of the liquid crystal display. Therefore, how to reduce the cost and at the same time maintaining the balance of the currents has become an imminent issue to be resolved.